Venous thromboembolism (VTE, includes both venous thrombosis and pulmonary embolism) is a frequent complication among patients with cancer. However, there is surprisingly little data regarding the incidence and time course of VTE and the risk of recurrent VTE among patients with a specific malignancy defined by histologic type and stage. In addition, it is not clear to what degree age, sex, ethnicity, stage, histologic type, and treatment predict the development of VTE. This information is important because there is preliminary data suggesting that use of anticoagulants, such as warfarin or low molecular weight heparin, may be beneficial in the primary prevention of VTE among cancer patients. The specific aims of this application are: 1) to define a cohort of patients diagnosed with one of the ten most frequent cancers in California and to identify hospital-reported cases of VTE in this cohort by linking the California Cancer Registry with the California Patient Discharge Data Set; 2) to determine and compare the incidence and time course of incident VTE after diagnosis of the most frequent cancers in California; 3) to determine demographic, treatment- and disease-related risk factors associated with developing VTE after diagnosis of the most frequent cancers in California; 4) to determine predictors of death within two years of diagnosis of each of the ten most frequent cancers in California; and 5) to determine the incidence of recurrent VTE and re-hospitalization for bleeding within a six-month period after diagnosis of incident VTE and to compare this to the incidence in age- and sex-matched patients with VTE who do not have cancer. The hypothesis are: 1) a cohort of cancer patients who develop VTE can be identified through the California Cancer Registry and the California Patient Discharge Data Set; 2) there is a significant variation in the incidence and time course of incident VTE among the ten most frequent cancer diagnoses, and among the different stages of each of these malignancies; 3) for each type of cancer, there is ethnic variation in the incidence of VTE, and factors such as age, stage, and therapy, will influence the observed rates of VTE in cancer patients; 4) for all malignancies, the development of VTE within 2 years of diagnosis is an independent predictor of death within 2 years of diagnosis; and 5) patients with cancer who develop VTE have a higher incidence of both recurrent VTE and severe bleeding complications related to anticoagulation therapy compared to age- and sex-matched patients with VTE who do not have cancer. We propose to take advantage of our ability to merge the extensive and mature California Cancer Registry with the linked California Patient Discharge Data Set in order to examine these questions. Results of this research will provide important data regarding the natural history of VTE in cancer patients and serve as the basis for designing prospective studies aimed at primary prevention of VTE in high-risk groups.